If $x \bigtriangleup y = 6x+y$ and $x \diamond y = x-4y$, find $0 \bigtriangleup (-3 \diamond 6)$.
Answer: First, find $-3 \diamond 6$ $ -3 \diamond 6 = -3-(4)(6)$ $ \hphantom{-3 \diamond 6} = -27$ Now, find $0 \bigtriangleup -27$ $ 0 \bigtriangleup -27 = (6)(0)-27$ $ \hphantom{0 \bigtriangleup -27} = -27$.